Electronic speed arrangement for electrically operated power tools

ABSTRACT

A speed control arrangement for electrically operated power tools in which an electronic control circuit within the housing of the tool regulates the speed between no-load and full-load operation of the tool, so that the speed is held substantially constant. The rotor of the motor within the tool is mounted in combination with bevel gears so as to form an angle polishing machine for portable applications. A terminal block mounted within the handle of the portable tool interconnects the wiring between the motor and the electronic controlling circuit. The electronic circuit provides for the operation of the tool from a single-phase utility outlet, and will disconnect the motor from the line when the maximum allowable speed is exceeded.

United States Patent Kurt Panic Stuttgart Oberturkheim, Germany 825,760

May 19, 1969 June 15, 1971 Robert Bosch G.m.b.II

Stuttgart, Germany May 18,1968

Germany Inventor Appl. No. Filed Patented Assignee Priority ELECTRONICSPEED ARRANGEMENT FOR ELECTRICALLY OPERATED POWER TOOLS 4 Claims, 4Drawing Figs.

US. Cl 310/50, 310/68, 51/l70.2

Int.Cl H02k 7/14 Field of Search 310/68, 47, 50, 72, 174, 62, 83;318/327, 306; 51/1 70.2

References Cited UNITED STATES PATENTS Meyer 1,954,977 4/1934 Albertson5 H1702 1,976,499 10/1934 I-Iochstetter..... 310/327 2,273,626 2/1942Connell 5 H1702 2,553,688 5/1951 Thompson... 5 H1702 3,280,351 10/1966Wolter 310/50 3,424,961 l/l969 Leenhouts 318/327 3,458,793 7/1969Tsergas 310/68 Primary Examiner-D. X. Slin'ey Assistant Examiner-R.Skudy Attorney-Michael S. Striker ABSTRACT: A speed control arrangementfor electrically operated power tools in which an electronic controlcircuit within the housing of the tool regulates the speed betweennoload and full-load operation of the tool, so that the speed is heldsubstantially constant. The rotor of the motor within the tool ismounted in combination with bevel gears so as to form an angle polishingmachine for portable applications. A terminal block mounted within thehandle of the portable tool interconnects the wiring between the motorand the electronic controlling circuit. The electronic circuit providesfor the operation of the tool from a single-phase utility outlet, andwill disconnect the motor from the line when the maximum allowable speedis exceeded.

PATENTED Jun 1 5 I97! sum 1 o 3 INVENTOR:

Kurt PAULE his ATTORNEY ATENTEI] M15197! n eff FIGS INVENTOR:

Kur'f DAL) LE Y /I)/L or his ATTORNEY ELECTRONIC SPEED ARRANGEMENT FORELECTRICALLY OPERATED POWER TOOLS BACKGROUND OF THE INVENTION Thepresent invention resides in an electrically operated power tool,particularly an electrically driven polishing machine with built-inalternating current commutator motor. The arrangement includes anelectronic speed regulating device. Electrically operated power toolsare known in the art, in which electronic speed regulating arrangements,either built into the power tool or separate therefrom, providecontinuous variation in the motor speed between zero and a maximumvalue.

These conventional electrically operated power tools exhibit for everyset speed of the series-wound AC commutator motor, a disadvantage ofbeing considerably dependent upon the torque. Thus, in such operationofthese motorized power tools, the speed which may be set is very much afunction of the output torque. The advantage of adjusting the speed insuch conventional electrically operated power tools, therefore, is againlost for the most part, since the'set speed can only be maintained forthe idling state. When the tool is used under load, the speed dropsimmediately, and must be readjusted manually afterwards. Such arequirement is, however, not very practical. Aside from this, anyreduction in the speed of the conventional electrically operated powertools, is accomplished through a reduction in the applied power. .When,under these conditions, the tool is operated under load and the speed ofthe tool falls as a consequence of the applied load, the effect of thespeed reduction through decrease in the applied power is superimposedupon the effect of reduced speed due to load, so that an undesirableoperating speed is realized.

Accordingly, it is an object of the present invention to provide anelectronic circuitfor regulating the speed of electrically operatedpower tools with AC commutator motor, so that the speed remainssubstantially constant between the idling state and the maximumpermissible for load. In accordance with the present invention, thisobject is achieved by providing that the power output in the form of theproduct of the torque and speed, rises functionally so that at the upperlimit, the relationship between the conventional idling speed and theconventional load speed has the ratio of substantially 1.6:]. Although apower rise or increase of 60 percent may be possible in special cases,it is of advantage to limit most applications to approximately 40percent increase in power. This results from the condition thatoperation beyond this latter limit gives rise to more severerequirements with regard to the construction of'the windings and thecommutator for resistance against centrifugal forces. The operating lifeof the ball bearings, and the precision fabricating requirements,particularly from the viewpoint of balancing, are also factors whichmust be taken into consideration when exceeding this limit. It is alsopossible, of course, in portable polishing machines to use the samepower with less effort at higher load speeds, by pressing the polishingdisc less against the tool.

In accordance with the present invention, the electrically operatedpower tool also achieves, under varying load, operation at the sameoptimum cutting speed. As a result, higher power is developed, throughthe tool of the present invention. It also follows from the presentinvention that due to the substantially constant speed, even at highload torques, the motor becomes well cooled, a condition which isessential particularly at such higher loads. As a result of such coolingaction, the increased heat losses are removed effectively. The increasedheat losses result from the increased power of the motor. It is to benoted, in this regard, that the mass of air required is proportional tothe cooling fan speed, whereas the generated pressure varies as thesquare of this speed. A specific pressure drop is required for thepurpose of conveying the cooling mass of air through the power tool. Theheat transfer also rises with increase in air mass velocity. As aresult, the electrically operated. power tool, in accordance with thepresent invention, is also adapted to deliver the increased power alsoat full load.

As a result of the design of the present invention, the cooing effectwithin overload regions of operation, is also more favorable than inconventional electrically operated power tools. The present inventionalso prevents, through the electronic regulating arrangement, that highspeeds and overspeeding of the driving motor upon removal of the loadupon the power tool. The particular advantage in the use of the presentinvention resides that the power tools, especially portable polishingmachines, are not driven below the optimum cutting speed, as inconventional electrically operated power tools. The optimum cuttingspeed is substantially identical to the permissible surface speed of thetool, and must not be exceeded during the idling condition of the tool.

The electronic regulating arrangement of the present invention,furthermore, can serve to rapidly reduce the applied voltage to themotor when exceeding the permissible maximum torque, so that the motoris protected against overloads.

The electronic regulator of the preset invention can, furthermore,reduce the starting current of the AC commutator motor for correspondingincrease in the starting time, so that the power tool may be operatedfrom a single-phase utility outlet, without affecting the line fuses. Inaddition to this advantage of applying the power tool to a single-phaseline,

the tool is also a safer device during operation. Thus, since thestarting torque does not occur suddenly and at such magnitudes as inconventional power tools, the danger that the tool may be torn from thehand of the operator or user, is substantially eliminated.

SUMMARY OF THE INVENTION A motor speed control arrangement for use inconjunction with electrically operated power tools, particularlyportable polishing machines. An alternating current commutator motoroperates in conjunction with an electronic speed regulating arrangementor device which controls the motor speed for variable load conditions.The speed regulating device serves to maintain the output shaft speed ofthe motor substantially constant between no-load or idling conditionsand full load conditions at which the motor develops the maximumpermissible torque. When this maximum permissible torque is exceededthrough an excessive load, the electronic speed regulating device hasmeans for rapidly decreasing the voltage applied to the motor, so thatthe latter is protected against overload and damage conditions. Thespeed regulating arrangement, furthermore, attenuates the startingcurrent of the driving motor for corresponding increase in the startingtime, so that the electrically operated power tool may be operated froma single-phase utility outlet or power line. As a result of thisfeature, the line fuses are not actuated or affected. The electronicspeed regulating device, in addition, maintains the speed of the motorunaffected from line voltage fluctuations within the range of plus orminus 15 percent. The electronic speed regulating arrangement also hasprovision for disconnecting the driving motor from the power supplyline, when the maximum permissible rotational speed is exceeded by 10percent.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction, and its methodof operation, together with additional objects and advantages thereof,will be best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view through theaxis of rotation of the electrically operated power tool, and shows theinterior construction with the speed regulating arrangement and switchmounted in place, in accordance with the present invention;

FIG. 2 is a schematic wiring diagram of the power tool in the form of anangle polisher, ofFIG 1;

FIG. 3 is a graphical diagram and shows the starting current of theangle polisher of FIG. I, as a function of,:time; and

FIG. 4 is a graphical diagram and shows as a function of torque load thefollowing parameters: the feed voltage applied to the motor by the speedregulating arrangement; the motor speed; the motor speed without the useof a speed regulating arrangement of the present invention; the motorspeed of a conventional angle polisher.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In referring to the drawing,the expressions behind or in back of, used to describe the drawing,denote the direction toward the transmission cable. The expression infront of denotes the direction toward the angular drive, whereas theexpression below denotes the direction from the polishing disc spindle.The usage of the expression above," on the other hand, denotes theopposite direction of the latter.

The angle polisher shown in FIG. I has a handle I, an intermediatehousing 2, a housing 3 for the motor and made of plastic material, and ahousing 4 for the driving linkage. The parts are held together throughbolts and screws, not shown in the drawing. The handle I is formed ofsynthetic material, such as plastic, for example, and a hollow crosssection. At the back end of the handle, an elastic bushing 5 isinserted. A cable 6 passes through this bushing 5 and into the handle.Through a capacitor 7 of hollow construction, the cable 6 enters theinterior of the handle. The capacitor 7 serves as a filter type ofcapacitor. A terminal board 8 is secured within the interior of thehandle. A switch 9 is mounted above the terminal board, and on thehandle.

A speedregulating arrangement in the form of an electronic regulatingcircuit 10 is built into the intermediate housing 2. This regulatingcircuit 10 controls the feed voltage'of the driving motor in theconventional manner through phase control of both half waves. Alaminated stator member 12 is secured with bolts 11 within the motorhousing 3. This laminated stator member 12 carries a stator coil 13. Themotor housing 3 is closed-off through a wall 14 at its back end. Anopening 16 is provided through the center of this wall I4, and a numberof additional openings are arranged exterior to the central opening. Ametallic bearing 17 is injection molded into the central opening 16. Aball bearing or roller bearing 18 is inserted into the metallic bearing17. The interior ring of the ball bearing is slipped upon the shaft 19.The shaft 19 which is supported within the motor housing through theroller bearings 18, carries a commutator 20 in front of the roller orball hearing 18. This shaft 19, furthermore, carries a rotor member 21upon which a coil 22 is wound. The front end of the shaft 19 is insertedinto an insulating bushing 23 which is secured within the hollow-backend 24 of a shaft 25. The shaft 25 is held within a transverse wall 27of the driving linkage housing 4, through means of a bearing 26. Themotor housing 3 and the driving linkage housing 4 are assembled togetherthrough the application of anv intermediate flange 28. This flange whichis also designed in the form of an air-transmitting type of flange, hasa disc 29 arranged transverse or perpendicular to the axis of the rotor,a central opening 30 within this disc 29.

A cooling member or impeller 31 is mounted upon the back end 24 of theshaft 25 in front of the flange 28. The impeller 31 sucks heated air outof the motor and from the speed regulating arrangement. This heated airis then blown or forced to the exterior of the tool, by way of theopenings 32 of the driving linkage housing in accordance with thepresent invention. A bevel pinion 33 is mounted at the front end of theshaft 25. The bevel pinion engages a bevel gear 34 which, in turn, ismounted upon the shaft 35 for the polishing disc. The shaft for thepolishing disc is rotatably mounted in place through a roller bearing 36and a ball bearing 37, which in turn, are held within the housing forthe driving linkage. This shaft has an end portion 38 projecting frombelow of the driving linkage housing. The projecting portion 38 isdesigned so that the polishing disc may he mounted thereon. At the backend of the shaft 19, a safety arrangement I00 and a taehogenerator 10bare arranged as parts of the regulator 10. Since these parts are not theobject of the present invention, they are not further described and areonly representatively designated in the drawing.

In the diagram of FIG. 2 of the angle polisher, it may be seen that theleads of the cable 6 are connected to two terminals of a switch 9 withinthe interior of the angle polisher. Through the switch 9, these leadsmay be interrupted The movable contacts of the switch 9 corresponding tothe fixed terminals or contacts to which the leads of the cable 6 areconnected, lead to the capacitor 7. An electrode lies within thedielectric of this capacitor, and serves as a third conductor of acommonly referred to Y-connection. This electrode within the capacitor,serves as a ground connection, and is connected with the stator member12 of the motor, through the terminal board 8. A symmetricalrelationship is forced upon the capacitor through the application ofthis ground connection. One of the connections from the capacitor leadsto the electronic regulating circuit 10, by way of the terminal board.The other connections lead directly to the motor, through the terminalboard. The leads or connections from the electronic regulating circuitare also applied to the motor, by way of the terminal board.

The solid curve in FIG. 3 shows graphically the current requirement ofthe angle polisher of FIG. 1, when in the idling state. The curve indashed or broken lines denotes the current requirement of an anglepolisher without speed regulating means, for comparison purposes. Thisgraphical representation refers to measurements taken on apparatuses ormachines in service, and shows that for the conventional polishers, thestarting current rises rapidly to approximately seven times theeffective nominal current. After reaching this peak value, the currentdrops rapidly, and falls below the effective nominal current after about0.8 seconds from the instant that the machine was switched on. Thecurrent in the conventional machine then tends asymptotically towardsthe current corresponding to the idling value. In the angle polisher, inaccordance with the present invention, on the other hand, in which aregulating arrangement is included in the form of an electronicregulating circuit, the current rises only to approximately 2.5 timesthe effective nominal current value. After approximately 2 seconds, thiscurrent in the machine of the present invention drops below theeffective nominal value. Through the combined reduction in the magnitudeof a current when starting, and increase in the starting time, it ispossible to operate the angle polisher of the present invention, from asingle-phase utility outlet, without affecting the line fuses.

FIG. 4 shows graphically the relationship of the feed voltage U which isapplied to the motor through the electronic regulating circuit, as afunction of the load torque M in foot lbs. The graphical representationshows that this feed voltage increases with load until the attainment ofa torque which is approximately one and a half times the nominal value.After that, the voltage drops readily until the torque corresponding totwice the nominal value is reached. At that point, the regulator shiftsand reduces also the feed voltage with decrease in load torque. Thespeed n, of the angle polisher, which is also superimposed upon thegraphical representation of FIG. 4, remains nearly unreduced withincreased load torque and increased feed voltage U,.,,, from idlingstate to nominal load. Within this region, the speed n drops onlyapproximately 5 percent. This speed, on the other hand, drops somewhatmore severely between the nominal load and the load which corresponds toone and a half times this nominal value. Within the range of the nominalload and the load which corresponds to twice the nominal value, therotational speed drops approximately 23 percent. After that, the speeddrops rapidly to zero, at which a stall torque prevails at approximatelythree-quarters of the nominal load value. As a result, a correspondingstall feed voltage remains.

The speed relationship n, ofthc same angle polisher, but without speedregulating means, is represented through dashed or broken lines. In thiscase, the rotational speed drops from the idling state to the nominalvalue or nominal load torque, by approximately 30 percent. This samesituation applies for the speed function n shown by dash-dot lines,corresponding to an angle polisher which is conventional in the trade orart. The speed of such a conventional device, is represented by thefunction designated n is substantially below the speed'of theelectronically regulated angle polisher. From the difference between thedashed curves and the dashdot curve, it is possible to observe that theangle polisher provided with electronic speed regulating means isdesigned so that it has a load speed which is substantially in theproximity of the conventional idling speed, heretofore.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied inelectrically operated power tools, it is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

What I claim as new and desire to be protected by Letters Patent is setforth in the appended claims:

1. An electrical power tool with electronic speed control arrangementcomprising, in combination, a motor with speed to be controlled whendriving a variable load between no-load and full load operation of saidmotor; electronic speed regulating means connected to said motor formaintaining the rotational speed of said motor substantially constantbetween no load and full load operation of said motor; a housing forenclosing said electronic speed regulating means integral with saidmotor; a handle member joined to said housing; and a terminal blockmember within said handle for holding connections between said motor andsaid electronic speed regulating means.

2. The motor speed control arrangement as defined in claim 1 includingbearing means within the housing for mounting rotatably the rotor ofsaid motor; cooling impeller means mounted on said rotor and rotatingtherewith for cooling said motor; and output driving linkage meansconnected to said rotor for driving a load.

3. The motor speed control arrangement as defined in claim 2 whereinsaid output linkage means comprises a bevel pinion mounted on saidrotor; and a bevel gear in mesh with said bevel pinion, whereby theoutput axis of speed rotation is perpendicular to the axis of rotationof said rotor.

4. The motor speed control arrangement as defined in claim 3 includingan output shaft driven by said bevel gear and having a threaded portionfor threadably receiving a polishing disc, whereby said motor speedcontrol arrangement is operable as an angle polisher.

2. The motor speed control arrangement as defined in claim 1 including bearing means within the housing for mounting rotatably the rotor of said motor; cooling impeller means mounted on said rotor and rotating therewith for cooling said motor; and output driving linkage means connected to said rotor for driving a load.
 3. The motor speed control arrangement as defined in claim 2 wherein said output linkage means comprises a bevel pinion mounted on said rotor; and a bevel gear in mesh with said bevel pinion, whereby the output axis of speed rotation is perpendicular to the axis of rotation of said rotor.
 4. The motor speed control arrangement as defined in claim 3 including an output shaft driven by said bevel gear and having a threaded portion for threadably receiving a polishing disc, whereby said motor speed control arrangement is operable as an angle polisher. 